1. Field of the Invention
Exemplary embodiments of the present invention relate to a digital cumulative spectrum analysis apparatus and method for direction finding (DF) and location; and, more particularly, to a digital cumulative spectrum analysis apparatus and method for DF and location using radio waves.
2. Description of Related Art
In general, electromagnetic waves which are energy generated from electric and magnetic flows are also referred to as radio waves. That is, when vibration occurs as electricity flows, an electric field and a magnetic field are generated at the same time. The electric field and the magnetic field periodically change to generate electromagnetic waves. Such electromagnetic waves always exist around us.
Since electromagnetic waves exist anytime and anywhere, various interferences occur among devices using electromagnetic waves. Therefore, devices such as mobile phones, which operate at an allocated frequency band, should be manufactured in such a manner that interference caused by the leakage of radio frequency (RF) into contiguous frequencies does not occur. However, since digital RF units, e.g., mobile phones, wireless LAN devices, Digital Multimedia Broadcasting (DMB), and RF Identification (RFID) devices exist on a wireless network, it is not easy to prevent interference among devices. Devices operating at the license-exempt band should normally operate even though interference exists. Furthermore, in order to reduce the interference, it is necessary to transmit output of devices with a low power for a short period.
The respective RF systems have the same amount of radio resources in all areas. However, a certain RF system may have an insufficient amount of radio resources in the same specific area, and another RF system may not be used. Therefore, the new type of RF technique such as Software-Defined Radio (SDR) and a Cognitive Radio (CR) has been researched in order to solve the above-described problems.
The SDR and CR are technologies which minimize the interference among devices to effectively use a limited radio spectrum. To effectively use the radio spectrum even in a complicated and diversified radio environment with the development of the RF technologies, measurement equipments to monitor RF services should reliably detect and analyze RF signals having a low power and a short duration time, and find the position of an interference which is to be removed.
A spectrum analyzer may be taken as an example of the device for detecting and analyzing RF signals. The spectrum analyzer measures time-domain signals at a frequency domain, and displays the measured signals on a screen. The spectrum analyzer may transform an RF signal from the time domain to a frequency domain through Discrete Fourier Transform (DTF) so as to calculate the magnitude of the signal at the frequency domain.
The spectrum analyzer displays the intensities of signals for each frequency component. At this time, a horizontal axis may be expressed by the unit of kHz/Div or MHz/Div which is referred to as a horizontal-axis frequency span (span/div).
However, such a spectrum analyzer has a sweep time during which a signal returns to a start point during the measurement of the signal. Therefore, since the measurement of signal is performed discontinuously, a certain signal may be omitted. When the omitted signal contains important information, the information may not be recognized. Furthermore, since the existing digital spectrum analyzer for direction finding has a limit in the number of spectrums per frame on a display, a data loss may occur when the data is processed at a high rate. In addition, the existing digital spectrum analyzer for direction finding could not observe a low-level signal around noise floor or a low-level signal with a high-level wideband signal.
In an existing fixed or portable direction finding system using the rotation of directional antennas, an operator should perform scanning and averaging for several times, in order to accurately estimate the direction of a signal.
FIGS. 1 and 2 illustrate a bearing-to-level waveform displayed by the existing digital spectrum analyzer for direction finding.
FIG. 1 illustrates a bearing-to-level waveform at a current mode displayed by the existing digital spectrum analyzer for direction finding, and FIG. 2 illustrates a bearing-to-level waveform at a maxhold mode displayed by the existing digital spectrum analyzer for direction finding.
Referring to FIGS. 1 and 2, the existing digital spectrum analyzer for direction finding can display only a single waveform at an update rate of several tens of frames per second. Therefore, a data loss may occur when the data is processed at a high rate by the spectrum analyzer.